Adjustable strength electro-magnet with constant air gap



Dec. 16, 1969 H. R. SHAFFER 3,484,728

ADJUSTABLE STRENGTH ELECTRO-MAGNET WITH CONSTANT AIR GAP Filed Aug. 2l, 1967 2 Sheets-Sheet l /f/ f/f/ @7 A Dec. 16, 1969 H, SHAFFER 3,484,728

ADJUSTABLE STRENGTH ELECTRO-'MAGNET WITH CONSTANT AIR GAP Filed Aug. 21, 1967 2 Sheets-Sheet 2 ZM M I N VENTOR.

Afm/ifea if MHP/Hz United States Patent 3,484,728 ADJUSTABLE STRENGTH ELECTRO-MAGNET WITH CONSTANT AIR GAP Howard R. Shaffer, Glenside, Pa., assignor, by mesne assignments, to ll-T-E Imperial Corporation, Philadelphia, Pa., a corporation of Delaware Filed Aug. 21, 1967, Ser. No. 662,113 Int, Cl. H01h 9/00, 7/08, 7/13 U.S. Cl. 335-176 11 Claims ABSTRACT F THE DISCLOSURE An adjustable strength electro-magnet with a constant air gap comprising a body portion magnetized by current ilowing through an adjacent circuit and an armature biased away from and movable toward the body portion when the magnetic attraction is sufficient; a constant air gap between magnet body and armature, a first spring for biasing the armature away from the body portion; a second spring biasing the armature toward the body portion and acting in opposition to the first spring; means for adjusting the biasing force of the second spring comprising a pivotable lever engaging one end of the spring and a flange having portions of varying height which dierent portions pivot the lever to various positions, correspondingly varying the biasing force of the second spring, thereby Calibrating the magnet armature to move when the ampere-turns level in the circuit adjacent the magnet body exceeds a predetermined Value; the armature having means connected with it, which means is engageable with the tripper bar of a circuit breaker for providing instantaneous magnetic trip thereof.

This invention relates to an adjustable strength electromagnet having a constant air gap between magnet body and armature, and more particularly, to a Calibrating means for the magnet for varying the ampere-turns level that must be exceeded in the electric circuit actuating the magnet before the magnet armature begins to move.

Prior art electro-magnetic devices employing an armature are calibrated by adjusting the length of the air gap between the armature and the body of the magnet. However, air gap adjustments must be made to criticaldimensions and may be diicult to make accurately in the field.

This invention relies on the principle that the force that restrains the movement of the armature of an electro-magnet, which force determines the ampere-turns level in the actuating electric circuit of the magnet that must be exceeded before the armature moves, can be varied by altering the force exerted on the magnet armature by a biasing device comprised of two biasing means, such as springs, acting in opposition to each other, thereby calibrating the magnet to operate at different ampere-turns levels.

The invention comprises a magnet body whih is adjacent a conductor in the circuit to which the magnet is to be responsive. An armature is spaced away from the bod a constant distance.

A first biasing means is employed for biasing the armature away from the body portion. A rst magnetic attraction in the magnet body on the armature, determined by the ampere-turns in the circuit, is required to overcome the strength of the first biasing means and draw the armature to the magnet body.

A second biasing means is also provided and is posi- 3,484,728 Patented Dec. 16, 1969 tioned with respect to the armature to operate in oppositionv to the iirst biasing means. The first biasing means determines the maximum ampere-turns that could be required for the particular magnet being considered to move the armature toward the body. The second biasing means, acting in opposition to the first biasing means, reduces the ampere-turns necessary to actuate the magnet, and thereby determines the minimum ampere-turns that could be required to move the armature toward the body. The biasing means may each be a spring. Each biasing means may be supported at its first end on a separate nut which is longitudinally movable along a threaded shaft. Adjustment of the respective nut for each of the biasing means will initially calibrate the biasing force of the respective biasing means. The magnet is initially calibrated by adjusting the position of the nuts against which the biasing means press. Later the magnet may be calibrated in the field by adjusting the button operated calibration means to be described.

The second biasing means, the one that biases the armature toward the magnet body, may be calibrated at any time, and in the field, by a lever means which presses against the second end of the vsecond biasing means. An annular flange is provided having a lower surface which engages the lever. The surface extends varying distances yfrom a fixed support provided for it and pivots the lever to varying extents, which charges the second biasing means to a corresponding extent.

The magnet of the present invention may be employed whenever an adjustable strength magnet is desired. The magnet is herein illustrated in conjunction with a circuit breaker of the type shown in U.S. Patent No. 3,155,802, issued on Nov. 3, 1964 to E. Wortmann, entitled U- Shaped Cradle for Circuit Breaker, and assigned to the assignee of this invention, but it may be used in any circuit breaker having a magnetic trip device, or in any other device requiring an adjustable strength magnet. When the magnet is used in a circuit breaker, the magnet armature, or a means connected with that armature is positioned to strike the circuit breaker tripper bar or other tripping means for initiating tripping of the circuit breaker.

Accordingly, it is a primary object of the present invention to provide an adjustable strength magnet.

It is another object of the present invention to provide such a magnet having a constant air gap between the magnet armature and the magnet body.

It is another object of the present invention to provide a magnet in accordance with the foregoing objects wherein the magnet armature is biased away from the magnet body by the combined force of two biasing means acting in opposition to each other and wherein the biasing force of at least one of the biasing means is adjustable.

It is another object of the present invention to provide an adjustable strength magnet which may be readily calibrated in the field.

It is a further object of the present invention to provide a magnet in accordance with the foregoing objects wherein a choice of two biasing means to act in opposition and of an air gap between magnet body and armature can determine the full range of operation for the magnet.

It is a further object of the present invention to provide an adjustable strength electro-magnet having a constant air gap for use in a circuit breaker.

These and other objects of the present invention will become apparent after a reading of the following description of the accompanying drawing in which:

FIG. 1 is a view in elevation of a magnet designed in accordance with the teachings of the instant invention, and is the view in the direction 11 of FIG. 2;

FIG. 2 is a side View of a magnet designed in accordance with the teachings of the instant invention;

FIG. 3 is a plan view, in the direction 3-3 of FIG. 1, of the magnet shown in FIG. 1;

FIGS. 4-6 schematically show the magnet of the present invention calibrated at various ampere-tum levels; and

FIG. 7 shows the magnet of the present invention mounted in a circuit breaker.

Referring to the figures, and particularly to FIGS. 1

and 2, the electric conductor 10 passes adjacent the magnet body 11, which is comprised of magnetizable material, whereby the alternating current in the conductor induces a magnetic field in and around magnet body 11. A variation in the ampere-turns level in the conductor 10 correspondingly varies the strength of the magnetic field induced in and around magnet body 11.

Conductor 10 has an aperture 10a therethrough and magnet body portion 11 has an aperture 11a therethrough, both of which apertures cooperate in the positioning of armature supporting shaft 25, as will be described. The arm 18 has an aperture 19 passing therethrough for permitting the through passage of a later described shaft 25.

Positioned in apertures 11a, 10a and 19 is shaft 25. The apertures are of sufficient diameter to permit free longitudinal translation of shaft 25 along its own axis. Fixedly secured to shaft 25 is armature 26 which is comprised of a magnetizable material, such as steel, which is attracted to magnet body 11 when the latter is magnetized. Armature 26 is held, by a biasing means 34 to be described, against arm 18 of bracket 15. A gasket or bumper device may separate these elements. Since armature 26 is supported against a fixed element, such as bracket arm 18, a constant air gap 28 is maintained between armature 26 and the opposing surface 29 of magnet body 11.

The shaft may be threaded along at least a portion of its surface and adjustable nuts 31 and 32, each having tapped threaded apertures therethrough, are positioned on shaft 25, in opposed relationship to opposite surfaces of armature 26. The nuts are adjustably positionable along threaded shaft 25. This aids in the calibration of the magnet during the manufacturing process as will be described. For the objects of the present invention to be realized, nuts 31 and 32 need not be adjustable in position, since calibration of the magnet in the field which is one of the objects of this invention does not require adjustment of nuts 31 and 32.

A biasing means 34, illustrated as being a compression spring, has a first end that seats on the nut 32. The opposite end seats against stationary seating surface 35 on the interior of body 11. Shaft 25 passes through spring 34. Spring 34 biases nut 32, and thus shaft 25, upward, as viewed in FIG. I, thereby biasing armature 26 against fixed arm 18 of bracket 15. Spring 34 exerts a first biasing force. If nut 32 is adjustable, the first biasing force may be adjusted during manufacture of the magnet in accordance with the specific application for the magnet. A predetermined ampere-turns level must be exceeded in conductor 10 adjacent magnet body 11 before the magnetic attraction exerted by body 11 upon armature 26 is suflicient to overcome the biasing force of biasing means 34 and to draw armature 26 against seating surface 29 of magnet body 11.

A second biasing means 37, illustrated as being a compression spring, is positioned to act in opposition to spring 34. One end of spring 37 seats on nut 31 and the other end is seated on a seating portion 38 of hereinafter described pivotable lever 40. Shaft 25 passes through spring 37.

Since spring 37 is unable to move seating portion 38, it biases nut 31 and thus, shaft 25 with a second biasing force to counter the first biasing force exerted by spring 34, and thereby reduces the magnetic attraction that must be exerted by body 11 upon armature 26 to draw the same for the invention to operate, the second biasing force of spring 37 must be less than the first force of spring 34.

If nut 31 is adjustable, the second biasing force may be adjusted during manufacture of the magnet. The choice of biasing forces for springs 34 and 37 determines, re-

`spectively, the maximum and the minimum ampere-turns level that must be exceeded in magnet body 11 before armature 26 will move. Different applications for a single magnet may require different biasing forces in springs 34, 37. Nuts 31, 32 can be positioned to initially calibrate the biasing force, respectively, of springs 37, 34. Thus, a standard spring may be used in different magnets where different biasing forces are required, instead of necessitating manufacture of many different strength springs.

While the biasing means 34 and 37 are shown positioned above opposite surfaces of the armature 26, it is within the contemplation of the present invention to have both operative biasing means 34, 37 on only one side of the armature 26, so long as the first and second biasing means operate in opposition to each other and so long as the biasing force of at least one of the biasing means is adjustable by a separate adjusting means to be described.

Pivotable lever 40 is provided for Calibrating the magnet in the eld and after manufacture is completed. Lever 40 is pivotable around its pivot 41 located on bracket 15. As lever 40 pivots counterclockwise, as viewed in FIG. 1, spring 37 will be compressed to a greater extent, i.e. it will be charged, and the second biasing force will increase with respect to the first biasing force of spring 34, whereby a lesser ampere-turns level in conductor 10 near magnet body 11 will actuate armature 26. Conversely, when lever 40 is pivoted clockwise, as viewed in FIG. l, spring 37 will be partially released, and its Ibiasing force against the bias of spring 34 will be reduced, whereby a greater ampere-turns level in conductor 10 will be required to actuate armature 26.

Referring to FIG. 3, it is to be noted that portion 38 of lever 40 consists of prongs 39 which form a slot between them, and which extend around but do not contact shaft 25. As the lever 40 is pivoted, its portion 38 moves left and right, as viewed in FIG. 3, with respect to shaft 25. Employing prongs 39 prevents the portion 38 of lever 40 from contacting shaft 25 which would undesirably cause the shaft to translate along its axis.

Lever 40 has a lobe 42 which is in engagement with the underside of an annular flange 44 attached to the rotatable button 45. Narrowed portion 45a of button 45 joins button 45 to flange 44 and passes through aperture 46 in arm 16 of--bracket 15.

Since flange 44 is annular, for it to engage the lever lobe 42, the lobe must be positioned beneath the flange. As shown in FIGURE 3, lobe 42 is on the side of lever 40 closer to prong 39b, whereby the lobe engages the annular depending flange 44.

As shown in FIG. 1, flange 44 extends downward from bracket arm 16 various distances at various annular surface positions. At 44a, the flange has a surface which extends down a minimum distance; at position 44b, the flange surface extends down an intermediate distance; and at position 44C the flange surface extends down a greater distance. By rotation of button 45, eg., by placing and rotating a screwdriver in notch 47, flange 44 is annularly rotated with respect to arm 16 and the different surfaces of flange 44 are brought into contact with lobe 42, thereby depressing lobe 42 of lever 40 to varying extents. Thus, button 45 and flange 44 serve as a lever position device.

As lobe 42 is depressed, it pivots lever 40` counterclockwise, as viewed in FIG. l, thereby increasing the compression of spring 37. As lobe 42 is permitted to rise, the normal bias of spring 37 will cause arm 38 of lever 40 to pivot upward and clockwise, thereby lessenng the biasing force of spring 37.

While the magnet is specifically described with lever 40 engaging spring 37 and spring 34 having a greater biasing force than spring 37, it is within the contemplation of the invention to have the spring which biases the magnet armature toward the magnet body (spring 37 in FIG. 1) have a biasing force greater than or equal to the biasing force of the spring which biases the armature away from the magnet body (spring 34 in FIG. 1) and to have the pivotable lever operate upon the spring biasing the armature away from the magnet body (spring 34 in FIG. 1). The spring biasing the armature away from the magnet could then have its biasing force adjusted to cooperate with the counterforce exerted by the spring biasing the armature toward the magnet body, so that the armature would be held away from the magnet with the proper force.

Refer to FIGURES 46 which show a magnet, such as that shown in FIGS. 1-3, in various operative positions. Corresponding elements in FIGS. 1-3 and 4-6 are correspondingly numbered.

In FIG. 4, the magnet there shown is calibrated in the position illustrated in FIGS. 1 3. Surface 44b of flange 44 is in engagement with lobe 42 of lever 40'. Biasing means or spring 34 exerts a continuous first biasing force pressing armature 26' against abutment 20'. In the illustrated rotative position of portion 38' of lever 40', biasing means or spring 37 exerts a second downward force in opposition to spring 34. Therefore, the biasing force of spring 37 reduces to an extent the effect of the biasing force of spring 34 on armature 26. In this position of flange 44', a rst ampere-turns level must be exceeded in conductor before the magnetic attraction of armature 26 by magnet body 11' is suflicient to overcome the biasing force of spring 34', as reduced by the biasing force of spring 37.

Referring to FIG. 5, flange 44' has been rotated so that surface 44e thereof is in engagement with lobe 42' of lever 40. Since surface `44C extends downward from mounting arm 16 a greater distance than does surface 44b, lobe 42 is depressed further, thereby pivoting lever 40 further downward, as viewed in FIG. 5, about its pivot 41', which increases the compression of spring 37', thereby increasing the force spring 37 applies in opposition to the biasing force of spring 34. A lesser ampereturns level need be exceeded in conductor 10', when flange 44 is in its position of FIG. 5 than when it is in its position of FIG. 4 to magnetically attract armature 26' to magnet body 11.

Referring to FIG. 6, flange `44 has been rotated so that surface 44m thereof is in contact with lobe `42 of lever 40. Surface 44a extends downward from bracket arm 16 a shorter distance than does either surface 44b or surface 44C. Accordingly, lobe 42' is depressed to the least extent when surface 44a is in contact with it. Biasing means or spring 37 biases pivoting lever 40 clockwise, as viewed in FIG. 6, so that'lobe `42 remains in contact with surface 44a. The force now exerted by spring 37 in opposition to the force exerted by spring 37 in either of the positions of FIG. 4 or 5, and in order to magnetically attract armature 26 toward magnet body 11', a greater ampere-turn level need be exceeded in conductor 10', when flange 44 is in its position of FIGURE 6 than when it is in its positions of FIGURE 4 or 5. It is obvious that additional flange surfaces at other distances from the arm 16 may be provided.

Note that between each of the surfaces 44a', 44b and 44C there are inclined flange surface portions connecting flange surfaces 44a', 44h', and 44C. While button 45 is designed to be rotated to calibrate the magnet at one of three ampereturns levels, where one of surfaces 44a', 44b', and 44e is in engagement with lobe 42', the magnet may be calibrated at intermediate ampere-turns levels by rotation of button 45 such that lobe `42 engages flange 44' at one of the intermediate inclined surfaces.

There has been shown an adjustable strength magnet which is readily calibrated in the field. Regardless of the calibration of the magnet, the air gap 28 between the armature 26 and the magnet body 11 remains constant.

Referring to FIG. 1, when armature 26 moves toward magnet body 11, shaft 25, which is secured to armature 26, moves with armature 26 toward the magnet. Shaft 25 may have a means 50 thereto secured which moves with the shaft. Means 50, as shown in FIG. 1 is an adjustable nut which may engage an object, such as the tripper bar of a circuit breaker, to cause the object to move when the magnet armature moves. Alternatively, a means for engaging an object may be secured to the armature 26.

FIG. 7 illustrates one application of the adjustable strength magnet of the instant invention. The circuit breaker `60 is typically a three phase unit including a molded housing, comprising base 61 and removable cover 62. The breaker is partitioned into three parallel elongated chambers, with only the center chamber being illustrated. Each chamber has identical current carrying elements, one for each phase of the circuit breaker, and in addition, the center chamber has a single contact operating mechanism for all three phases.

Each of the current paths comprises load terminal connector 66, load terminal strap 67, conductor 10, loop forming portions 68 and 100, lug 72, flexible member 73, movable contact arm 74, movable contact 75, stationary contact 76, line terminal strap 77, and terminal connector 78 which is secured by screw 79 to line terminal strap 77. Arc-chute 80 is positioned to receive electric current arcs drawn between cooperating contacts 75, 76 upon their parting.

Mechanism 80 for contact operation is of a type well known in the art' and is described in U.S. Patent No. 3,155,802, issued to E. Wortmann on Nov. 3, 1964, entitled U-Shaped Cradle for Circuit Breaker, and assigned to the assignee of the instant invention. Briefly, operating mechanism 80 includes handle 81, which projects through cover opening 82, for manually operating cooperating contacts 75, 76 into and out of engagement. Handle 81 is mounted to the web of inverted U-shaped member 83 which is pivotally mounted at 84 to U-shaped frame 85. A pair of main springs 86 extends from the web of U- shaped member 83 to triangular member 87 which is pivotally mounted to the knee 88 of the toggle linkage comprising links 89, 90.

The lower end of the link 90 is pivotally connected at 92 to bracket 93 which carries contact arm 74. The upper end of link l89 is pivoted at 94 to latchable cradle 95. Transverse tie bar 96 extends through all three of the breaker housing compartments and carries the brackets 93 of all three phases so that the movable contacts of all three phases are simultaneously operated into and out of engagement with their cooperating stationary contacts 76.

Cradle 95 carries latch member 101 in engagement with portion 102 of auxiliary latch member 103 which is pivoted to frame 85 at 104. Latch 105 of auxiliary latch member 103 is engageable with main latch member 106 carried by transversely extending common tripper bar 107. When tripper bar 107 is pivoted clockwise, latch tip is released, in turn releasing latch member 101, thereby permitting cradle 95 to pivot counterclockwise about its pivot 108 to collapse toggle 89, 90 so that springs 86 separate contacts 75, 76.

The magnet of the present invention is mounted in the above described circuit breaker. Similar elements to those shown in FIGS. 1-3 are similarly numbered in FIG. 7. Mounting block 14 is either secured to or integral with circuit breaker base 61. Portion 10 of conductor strap 67 passes between the arms of magnet body 11 in the manner shown in FIG. l. As shown in FIG. 7, armature 26 has a rigid extending element 110 attached to it which moves toward magnet body 11 when armature 26 is so moved. Adjusting screw 111 passes through extending element 110 and when armature 26 is attracted by magnet body 11, adjusting screw 111 engages the downward extension 112 of tripper bar 107 to cause a clockwise rotation thereof for releasing of the circuit breaker latches.

It is within the contemplation of the invention to position mounting block 14, and portion 10` of terminal strap 67 further to the left, as viewed in FIG. 7, and to make of greater length the extending portion 112 of tripper bar 107, whereby nut 50 attached to shaft 25 might be the element that engages the downward extension 112 of tripper bar 107. Alternatively, rigid element 110 might be attached to nut 50 for engaging the extending portion 112. It is the movement by armature 26 of an element connected with either armature 26 or shaft 25, to which armature 26 is xedly attached, that brings the element into engagement with downwardly extending portion 112 of tripper bar 107 and causes tripping of the circuit breaker when a pre-determined ampere-turns level in magnet body 11 and in conductor 10 is exceeded. When used in a circuit breaker, such as circuit breaker 60, the magnet of the present invention serves as an instantaneous magnetic tripping mechanism.

There has just been described an adjustable electromagnet having a movable armature that is spaced apart from the magnet body by a constant air gap. The magnet is calibratable to enable the armature to move toward the magnet body only when a pre-determined ampereturns level in a conductor adjacent the electro-magnet body has been exceeded. Adjustability is obtained by providing a first compression spring which biases the armature away from the magnet body and a second compression spring which operates in opposition to the first compression spring and reduces the force exerted by the first spring.

Although this invention has been described with respect to its preferred embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art, and it is preferred, therefore, that the scope of the invention be limited not by the specific disclosure herein, but only by the Iappended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. An adjustable strength electro-magnet comprising:

a magnet body; means for magnetizing said body;

an armature support shaft; an armature supported on said shaft at a predetermined distance away from said body and being adapted to move with respect to said body when the latter is magnetized; the improvement comprising, said armature being movable with respect to said body, longitudinally with respect to said support shaft;

calibrating means connected with said armature for acting on said armature to adjust the strength of the magnetic field required to move said armature With respect to said body; said calibrating means comprising a first biasing means for biasing said armature in a first direction and a second biasing means which is operatively connected with said first biasing means for exerting a force in opposition to the force exerted by said first biasing means; said second biasing means being positioned and operative to vary the forceV exerted by said first biasing means on said armature; an adjusting means connected with said calibrating means for `adjusting the force exerted by said first and second biasing means on said armature; and

said armature having opposite sides, said first biasing means being located on and operating to exert a biasing force on one side of said armature and said second biasing means being located on and operating with respect to the opposite side of said armature; said biasing means each pressing against said armature.

2. The adjustable strength electro-magnet of claim 1, wherein the improvement further comprises,

said adjusting means comprising a first means for charging one of said biasing means to a varying extent.

3. The adjustable strength electro-magnet of claim 1,

wherein said first direction is away from said body;

the improvement further comprising, said adjusting means comprising a first means for charging said second biasing means to a varying extent.

4. The adjustable strength electro-magnet of claim 3, wherein the improvement further comprises, said adjusting means further comprising a second means for charging said first biasing means to a varying extent.

5. The adjustable strength electro-magnet of claim 3, wherein the improvement further comprises,

both said first and said second biasing means being connected with said armature.

6. The adjustable strength electro-magnet of claim 5,

wherein the improvement further comprises,

said second biasing means having a first and a second end; said first end of said second biasing means being connected with said armature;

a lever means in engagement with said second end of said second biasing means;

and a lever positioning device in engagement with said lever means for adjusting the position of said lever means, thereby adjusting the position of said second end of said second biasing means and the biasing force of said second biasing means upon said armature.

7. The adjustable strength electro-magnet of claim 6,

wherein the improvement further comprises,

said lever positioning device comprising an arm and an annular fiange support by and annularly rotatable with respect to said arm; said annular flange having a plurality of surfaces which extend various predetermined distances away from said arm; said flange being so positioned that during the operation of said magnet, one of said surfaces is in engagement with said lever means;

and a rotator connected with said ange for rotating same, whereby said ange positions said lever means in any of a number of pre-determined positions, thereby charging said second biasing means to a varying extent.

S. The adjustable electro magnet of claim 7, wherein the improvement further comprises,

a support for said lever means and a pivot for said lever means on said support, whereby each of the said surfaces of said flange cause said lever means to pivot to a different position.

9. An adjustable strength electro-magnet comprising,

a magnet body; means for magnetizing said body;

an armature supported a predetermined distance away from said body and being adapted to move with respect to said body when the latter is magnetized; and a support for said armature;

the improvement comprising,

calibrating means connected with said armature for acting on said armature to adjust the strength of the magnetic field required to move said armature with respect to said body;

said calibrating means comprising a biasing device for biasing said armature for movement with respect to said body; and an adjusting means connected with said biasing device for adjusting the force exerted by said biasing device;

said biasing device comprising a first biasing means for biasing said armature in a first direction away from said body and a second biasing means which is operatively connected with said first biasing means for exerting a force in opposition to the force exerted by said first biasing means;

said adjusting means comprising a first means for charging said second biasing means to a varying extent;

both said first and second biasing means being connected with said armature;

said second biasing means having a first and a second end; said first end of said secon-d biasing means being connected with said armature;

a lever means in engagement with said second end of said second biasing means;

and a lever positioning device in engagement with said lever means for adjusting the position of said lever means, thereby adjusting the position of said second end of said second biasing means and the biasing force of said second biasing means upon said armature;

said lever positioning device comprising an arm and an annular flange support by and annularly rotatable with respect to said arm; said annular fiange having a plurality of surfaces which extend various predetermined distances away from said arm; said flange being so positioned that during the operation of said magnet, one of said surfaces is in engagement with said lever means;

and a rotator connected with said flange for rotating same, whereby said flange positions said lever means in any of a number of predetermined positions,

, thereby charging said second biasing means to a varying extent;

a shaft passing transversely through said armature; said first biasing means having a first and a second end;

said shaft having thereon a third support for said first end of said second biasing means and a fourth support for said first end of said first biasing means; a stationary surface included in said magnet, which surface is engaged by said second end of said first biasing means;

said armature having opposite sides, said third and said fourth support elements being in opposed relationship to said opposite sides of said armature; said first and said second biasing means being away from one of said opposite sides of said armature; said third and said fourth support elements being adjustable along the length of said shaft for initially calibrating said magnet.

10. In a circuit breaker comprising movable and stationary cooperating contacts, an electric circuit in which said contacts are positioned, the circuit being the circuit to be protected by said circuit breaker, and a tripper for tripping apart said cooperating contacts;

an adjustable magnetic trip device comprising,

a magnet body; means connected with said circuit for magnetizing said body when an overload condition develops in said circuit;

an armature support shaft;

an armature supported on said support shaft a predetermined distance away from said body and being a-dapted to move along said support shaft with respect to said body when the latter is magnetized; said armature including engaging means for engaging said tripper to activate said tripper to trip apart said cooperating contacts;

the improvement comprising,

said armature being movable with respect to said body,

longitudinally with respect to said support shaft;

Calibrating means connected with said armature for acting on said armature to adjust the strength of the magnetic field required to move said armature with respect to said body;

said Calibrating means comprising a first biasing means for biasing said armature in a first direction and a second biasing means which is operatively connected with said rst biasing means for exerting a force in opposition to the force exerted by said first biasing means; and second biasing means being positioned and operative to carry the force exerted by said first biasing means on said armature;

an adjusting means connected with said Calibrating means for adjusting the force exerted by said first and second biasing means on said armature; and

said armature having opposite sides, said first biasing `means being located on and operating to exert a bias- Ling force on one side of said armature and said, sec- `ond biasing means being located on and operating with respect to the opposite side of said armature; said biasing means each pressing against said armature.

11. In a circuit breaker comprising movable and stationary cooperating contacts, an electric circuit in which said contacts are positioned, the circuit being the circuit to be. protected by said circuit breaker and a tripper for tripping apart said cooperating contacts;

an adjustable magnetic trip device comprising,

a `magnet body; means connected with said circuit for ,magnetizing said body when an overload condition ,develops in said circuit;

an armature supported a predetermined distance away from said body and being adapted to move with respectto said body when the latter is magnetized; and a support for said armature; said armature including engaging means for engaging said tripper to activate said tripper to trip apart said cooperating contacts;

the improvement comprising,

calibrating means connected with said armature for acting on said armature to adjust the strength of the magnetic field required to move said armature with respect to said body;

said calibrating means comprising a biasing device for biasing said armature for movement with respect to said body; and an adjusting means connected with said biasing device for adjusting the force exerted by said biasing device;

said biasing device comprising a first biasing means for biasing said armature in a first direction away from said body and a second biasing means which is operatively connected with said first biasing means for exerting a force in opposition to the force exerted by said first biasing means;

said adjusting means comprising a first means for charging said second biasing means to a varying extent;

both said first and second biasing means being connected with said armature;

said second biasing means having a first and a second end; said first end of said second biasing means being connected with said armature;

a lever means in engagement with said second end of said second biasing means;

and a lever positioning device in engagement with said lever means for adjusting the position of said lever means, thereby adjusting the position of said second end of said second biasing means and the biasing force of said second biasing means upon said armature;

said lever positioning device comprising an arm and an annular flange support by and annularity rotatable with respect to said arm; said annular flange having a plurality of surfaces which extend various predetermined distances away from said arm; said flange being so positioned that during the operation of said magnet, one of said surfaces is in engagement with said lever means;

and a rotator connected with said fiange for rotating same, whereby said flange positions said leve'r means in any of a number of predetermined positions, thereby charging said second biasing means to a varying extent;

a shaft passing transversely through said armature; said first biasing means having a first and a second end;

said shaft having thereon a third support for said first end of said second biasing means and a fourth sup- 11 12 port for said rst end of said rst biasing means; a length of said shaft for initially Calibrating said stationary surface included in said magnet, which magnet. surface is engaged by said second end of said first References Cited biasing means; UNITED STATES PATENTS said armature having opposite sides, said third and said 5 3 17 76 l 6 1 fourth Support elements being in opposed relation- 31804 136g lzlaer ship to said opposite sides of said armature; said first and said second biasing means being away from one BERNARD. A GILHEANY Primary Examiner of said opposite sides of said armature; said third and fourth support elements being adjustable along the 10 HAROLD BROOME Assistant Examiner 

